patch 8.1.0870: Vim doesn't use the new ConPTY support in Windows 10

Problem:    Vim doesn't use the new ConPTY support in Windows 10.
Solution:   Use ConPTY support, if available. (Nobuhiro Takasaki, closes #3794)
diff --git a/src/proto/terminal.pro b/src/proto/terminal.pro
index e6914c0..0fa62b7 100644
--- a/src/proto/terminal.pro
+++ b/src/proto/terminal.pro
@@ -57,4 +57,6 @@
 void term_send_eof(channel_T *ch);
 job_T *term_getjob(term_T *term);
 int terminal_enabled(void);
+void term_free_conpty(term_T *term);
+int use_conpty(void);
 /* vim: set ft=c : */